Schemata for reading and reading comprehension performance

Bibliography: leaves 51-56Supported by the National Institute of Educatio

Orbital selective crossover and Mott transitions in an asymmetric Hubbard model of cold atoms in optical lattices

We study the asymmetric Hubbard model at half-filling as a generic model to describe the physics of two species of repulsively interacting fermionic cold atoms in optical lattices. We use Dynamical Mean Field Theory to obtain the paramagnetic phase diagram of the model as function of temperature, interaction strength and hopping asymmetry. A Mott transition with a region of two coexistent solutions is found for all nonzero values of the hopping asymmetry. At low temperatures the metallic phase is a heavy Fermi-liquid, qualitatively analogous to the Fermi liquid state of the symmetric Hubbard model. Above a coherence temperature, an orbital-selective crossover takes place, wherein one fermionic species effectively localizes, and the resulting bad metallic state resembles the non-Fermi liquid state of the Falicov-Kimball model. We compute observables relevant to cold atom systems such as the double occupation, the specific heat and entropy and characterize their behavior in the different phases

Weak coupling study of decoherence of a qubit in disordered magnetic environments

We study the decoherence of a qubit weakly coupled to frustrated spin baths. We focus on spin-baths described by the classical Ising spin glass and the quantum random transverse Ising model which are known to have complex thermodynamic phase diagrams as a function of an external magnetic field and temperature. Using a combination of numerical and analytical methods, we show that for baths initally in thermal equilibrium, the resulting decoherence is highly sensitive to the nature of the coupling to the environment and is qualitatively different in different parts of the phase diagram. We find an unexpected strong non-Markovian decay of the coherence when the random transverse Ising model bath is prepared in an initial state characterized by a finite temperature paramagnet. This is contrary to the usual case of exponential decay (Markovian) expected for spin baths in finite temperature paramagnetic phases, thereby illustrating the importance of the underlying non-trivial dynamics of interacting quantum spinbaths.Comment: 12 pages, 18 figure

Monetary disorder and financial regimes - The demand for money in Argentina, 1900-2006

Argentina is a unique experience of protracted economic instability and monetary disorder. In the framework of a long-term view, we investigate the demand for narrow money in Argentina from 1900 to 2006, shedding some light on the existence of money demand equilibria in extremely turbulent economies. The paper examines the effect of monetary regime changes by dealing with the presence of structural breaks in long-run equations. We estimate and test for regime changes through a sequential approach and we embed breaks in long-run models. A robust cointegration analysis can be hence performed in a single-equation framework. We find that estimated parameters are in sharp contrast with those reported in the literature for Argentina, but in line with those reported for industrialized countries, while significant structural breaks appear consistent with major policy shocks that took place in Argentina during the 20th century.money demand ; financial regimes ; structural breaks ; single-equation cointegration ; cointegration test ; Argentina monetary history

Phase diagram of the asymmetric Hubbard model and an entropic chromatographic method for cooling cold fermions in optical lattices

We study the phase diagram of the asymmetric Hubbard model (AHM), which is characterized by different values of the hopping for the two spin projections of a fermion or equivalently, two different orbitals. This model is expected to provide a good description of a mass-imbalanced cold fermionic mixture in a 3D optical lattice. We use the dynamical mean field theory to study various physical properties of this system. In particular, we show how orbital-selective physics, observed in multi-orbital strongly correlated electron systems, can be realized in such a simple model. We find that the density distribution is a good probe of this orbital selective crossover from a Fermi liquid to a non-Fermi liquid state. Below an ordering temperature $T_o$, which is a function of both the interaction and hopping asymmetry, the system exhibits staggered long range orbital order. Apart from the special case of the symmetric limit, i.e., Hubbard model, where there is no hopping asymmetry, this orbital order is accompanied by a true charge density wave order for all values of the hopping asymmetry. We calculate the order parameters and various physical quantities including the thermodynamics in both the ordered and disordered phases. We find that the formation of the charge density wave is signaled by an abrupt increase in the sublattice double occupancies. Finally, we propose a new method, entropic chromatography, for cooling fermionic atoms in optical lattices, by exploiting the properties of the AHM. To establish this cooling strategy on a firmer basis, we also discuss the variations in temperature induced by the adiabatic tuning of interactions and hopping parameters.Comment: 16 pages, 19 fig

Induction of T Cell Immunity Overcomes Resistance to Pd-1 and Ctla-4 Blockade and Improves Survival in Pancreatic Cancer

Disabling the function of immune checkpoint molecules can unlock T cell immunity against cancer, yet despite remarkable clinical success with monoclonal antibodies (mAb) that block PD-1 or CTLA-4 resistance remains common and essentially unexplained. Certain tumors, especially pancreatic carcinoma, are fully refractory to these antibodies. As reported in this thesis, I used a genetically engineered mouse model of pancreatic carcinoma in which spontaneous immunity is minimal, and found that PD-L1 is prominent in the tumor microenvironment, a phenotype confirmed in patients. Tumor infiltrating T cells express PD-1 even more prominently than T cells in a classical model of chronic infection, in which anti-PD-1 mAb mediates clinical benefit. Despite this striking expression of PD-1 and PD-L1 in the pancreatic tumor microenvironment, treatment with anti-PD-1 mAb, with or without anti-CTLA-4 mAb, fails in well-established tumors, recapitulating clinical results. Agonist anti-CD40 mAb with chemotherapy, deployed as a vaccine, induces T cell immunity and reverses the complete resistance of pancreatic tumors to anti-PD-1 and anti-CTLA-4. The combination of anti-CD40/chemotherapy plus anti-PD-1 and/or anti-CTLA-4 induces regression of subcutaneous tumors, improves overall survival, and confers curative protection from multiple rechallenges, consistent with immune memory not otherwise achievable. Combinatorial treatment nearly doubles survival of mice with spontaneous pancreatic cancers, revealing a clinical opportunity. These findings suggest that in non immunogenic tumors, epitomized by pancreatic carcinoma, baseline refractoriness to checkpoint inhibitors may be rescued by the priming of a T cell response with an antitumor vaccine. These studies indicate that understanding the immunobiology of differing tumor types may improve the ability to rationally design combinatorial immunotherapies in oncology